The following code snippet is failing to compile on N := big.NewInt(n) with the following error:
cannot use n (variable of type int) as int64 value in argument to big.NewInt
func Factorial(n int) *big.Int {
var result = new(big.Int)
i := new(big.Int)
N := big.NewInt(n)
for i.Cmp(N) < 0 {
result = result.Mul(i, result)
i = i.Add(i, new(big.Int))
}
return result
}
If I pass an int64 literal (i.e., N := big.NewInt(1)), it works. But I need a way to convert an int64 variable or parameter/argument to a big.Int. What am I doing wrong? Does Go not support this at all?
The error is because the https://pkg.go.dev/math/big#NewInt function takes an int64 value as the argument and not an int type. Do the required type conversion as
N := big.NewInt(int64(n))
Moreover the computation logic can very simply written as
func Factorial(n int) *big.Int {
result, one := big.NewInt(1), big.NewInt(1)
bigN := big.NewInt(int64(n))
for bigN.Cmp(&big.Int{}) == 1 {
result.Mul(result, bigN)
bigN.Sub(bigN, one)
}
return result
}